In the manufacture of semiconductors, semiconductor devices are produced on thin disk-like substrates called wafers. Generally, each substrate contains a plurality of semiconductor devices. The importance of minimizing contaminants on the surface of these substrates during production has been recognized since the beginning of the industry. Moreover, as semiconductor devices become more miniaturized and complex due to end product needs, the cleanliness requirements have become more stringent. This occurs for two reasons.
First, as devices become miniaturized, a contaminating particle on a wafer will occupy a greater percentage of the device's surface area. This increases the likelihood that the device will fail. As such, in order to maintain acceptable output levels of properly functioning devices per wafer, increased cleanliness requirements must be implemented and achieved.
Second, as devices become more complex, the raw materials, time, equipment, and processing steps necessary to make these devices also become more complex and more expensive. As a result, the cost required to make each substrate increases. In order to maintain acceptable levels of profitability, it is imperative to manufacturers that the number of properly functioning devices per substrate be increased. One way to increase this output is to minimize the number of devices that fail due to contamination. Thus, increased cleanliness requirements are desired.
Accordingly, in the process of cleaning the surface of a substrate, a pressurized fluid can be supplied through a spray jet cleaning apparatus and applied continuously on the substrate surface in order to aid in the removal of contaminants on the substrate surface. The pressurized spray jet cleaning apparatus at times, however, may not be able to remove some contaminants or tiny particles on the substrate surface. The cleaning ability can thus be enhanced by raising the pressure of the fluid imparting higher velocity to the fluid as it exits the spray jet cleaning apparatus. However, the higher velocity fluid, while enhancing the cleaning ability of the spray jet cleaning apparatus, also increases the likelihood of damage to the substrate surface due to the force of the fluid or fluid droplets impacting the substrate surface.
Two-fluid spray jets may also be employed in the cleaning process. In using a two-fluid spray jet apparatus, a gas can be mixed with a fluid to form a cleaning mixture. The composition of the cleaning mixture, including the quantity and composition of any gas dissolved in the cleaning mixture, used in the substrate cleaning process can affect cleaning efficiency and the amount of damage caused to the substrate. However, two-fluid spray jets can also damage a substrate through cavitation of the gas bubbles on the substrate surface. This effect happens when the gas accelerated through the spray jet apparatus atomizes the fluid to form bubbles, these droplets then agglomerate together trapping gas under the agglomerated droplets especially as gas pressures are increased and collapse, i.e., implosion. During implosion of a bubble, the bubble tries to collapse from all sides. However, if the bubble is laying on or near a portion of the substrate surface or other material, it most often collapses towards the sensitive structure. This can cause substantial damage to the substrate surface to be cleaned.
However, if the spatial distance between droplets is increased, the inclination of the droplets to agglomerate can be minimized. One solution is to increase the internal diameter of the spray jet apparatus to much larger than 3.5 mm while using the same fluid flow rate. There are, however, disadvantages as the larger diameter spray jet apparatuses use a larger gas flow in order to achieve the same cleaning. This is not a preferred solution because the manufacturing fabrication site where the devices are made have a limit as to the amount of gas that can be used. About 90 psi is typically the maximum gas flow that can be supplied to a cleaning system.
Therefore, an idea such as that expressed in U.S. Pat. No. 5,918,817 where the gas would be approaching the speed of sound or acoustic velocity is not appropriate for general device manufacturing even when the internal diameter is near the 3.5 mm diameter. Also, a two fluid spray tends to create a turbulent effect when using the designs laid out in the above patent due to the area known as the mixing chamber. The mixing chamber is effective for breaking up the fluid into droplets but also consumes the material from the sidewall and makes using Teflon™ somewhat impractical due to wear. Teflon™ however is a preferred material from the device maker standpoint because of its chemical stability. The conical area in the mixing chamber may help to create mixing of gas and chemicals where mixing may not be preferred.
The invention disclosed in U.S. Pat. No. 6,048,409 is a spray jet apparatus that has a straight portion. This straight portion has a limiting effect as to the droplet size that can be created. This is addressed by supplying an outer ring of gas for an external small droplet formation and speed control. This increases the spatial distance between droplets to the detriment of the cleaning because only the droplets in the center flow are accelerated the fastest and are responsible for cleaning. This means a large portion of the fluid droplets forms a broadband mist reducing the overall efficiency of the spray jet yet the application to sensitive structures is maintained at the expense of cleaning. High cleaning efficiency is only maintained at above 100 m/s which is above the desired gas usage rate of device manufacturing, thereby requiring special gas delivery and not suitable for device damage control for Nano technology nodes.
Accordingly, there is a need for an improved spray jet cleaning apparatus and method that is able to provide effective cleaning efficiencies while minimizing damage to the surface of the substrate.